Evidence ofs-wave pairing symmetry in the layered superconductorLi0.68NbO2from specific heat measurements

Abstract

A high quality superconducting ${\mathrm{Li}}_{0.68}{\mathrm{NbO}}_{2}$ polycrystalline sample was prepared by deintercalation of Li ions from ${\mathrm{Li}}_{0.93}{\mathrm{NbO}}_{2}$. The field-dependent resistivity and specific heat were measured down to $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature dependence of the upper critical field is determined. A notable specific-heat jump is observed at the superconducting transition temperature ${T}_{c}\ensuremath{\sim}5.0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at zero field. Below ${T}_{c}$, the electronic specific heat shows a thermal activated behavior and agrees well with the theoretical result for the BCS $s$-wave superconductor. It indicates that the superconducting pairing in ${\mathrm{Li}}_{0.68}{\mathrm{NbO}}_{2}$ has $s$-wave symmetry.